Isotope separation

ABSTRACT

An isotope separation apparatus comprises a plurality of independent developing units, each comprising 2 to 20 adsorbent-packed columns forming a continuous developing circuit or passageway, and the developing units are connected to at least one common main pipe for supplying an isotope mixture solution, a regenerating agent solution, or an eluent solution. Also, in a further embodiment the developing units are connected to common liquid-discharge main pipes. 
     The separation or concentration of isotopes such as uranium isotopes, nitrogen isotopes, boron isotopes, etc., is performed by continuously developing the isotope mixture solution passed through the individual adsorbent-packed columns successively in each developing units.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and process for separatingisotopes. More particularly, it relates to an apparatus and process forseparating isotopes using a plurality of developing units connected toat least one liquid-supply main pipe.

2. Description of the Prior Art

In separating and concentrating an isotope from a mixture of isotopes onan industrial scale, a desired amount of separation and concentrationthereof is generally obtained by combining a large number of separationunits in the form of a network called a "cascade" since the separationfactor of a single isotope separator is usually very small. For example,Kunio Higashi; Uranium Concentration (published by Nikkan Kogyo ShinbunSha in 1971) teaches that in the case of producing 5% concentrateduranium-235 using natural uranium as the raw material by a gaseousdiffusion method, it is necessary to form a cascade by combining, inseries, separation units composed of 902 concentration stages and 500recovery stages. Also, in the case of producing the uranium isotope onan industrial scale by gas centrifuging, it is necessary to form acascade by combining, both in series and in parallel, several hundredthousands of centrifuges per plant and the entire separation apparatusused for this purpose is complicated and hard to control.

For example, either the cascade of 1400 stages in the gaseous diffusionunit or the cascade of several hundred thousand centrifuges acts as oneseparation apparatus where the stream of uranium hexafluoride gas ineach stage must be accurately controlled in order to maximize theseparation factor of the uranium isotope. Furthermore, if a part of alarge number of the separation units shuts down, the resultingdisturbance of the gas stream or the concentration of isotopes wouldextend all through the cascade. For recovering under the optimumseparation conditions, complicated calculations and operation controlmay be required. Still further, in order to slightly change the uraniumisotope concentration of a product by the operation, the concentrationmust be changed by controlling the operation conditions of each of themany separation units while trying to maximize the separation factor ofthe cascade.

In separating an isotope on an industrial scale, it has been a commonobservation that several thousands to several hundred thousandseparation units must be assembled into one cascade, which causesvarious difficulties in operation.

SUMMARY OF THE INVENTION

An object of this invention is, therefore, to provide a novel isotopeseparation apparatus which can overcome essentially the above-describeddifficulties in operation control.

Another object of this invention is to provide a process of separatingvarious kinds of isotopes using the novel apparatus.

That is, according to this invention, there is provided an isotopeseparation apparatus comprising at least two developing units, with eachdeveloping unit comprising at least two adsorbent-packed columns forminga continuous circuit and with each developing unit being connected to atleast one common liquid-supply main pipe through flow control devices.

Also, according to another embodiment of this invention, there isprovided an isotope separation process which comprises supplying asolution of an isotope mixture to each of the developing units of theabove-described isotope separation apparatus through one of theabove-mentioned common liquid-supply main pipes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a typical embodiment of the isotope separation apparatus ofthis invention;

FIG. 2 shows an example of the application of this invention using anactivating means for a regenerating agent and an eluent which areemployed in addition in the apparatus in FIG. 1;

FIG. 3 shows examples of pressure regulators in liquid-supplying mainpipes used in the apparatus of this invention;

FIG. 4 shows an example of a system of connecting liquid-discharge mainpipes and the developing units in this invention; and

FIG. 5 shows the developing units employed in Example 1 givenhereinafter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An isotope separation process in a single developing unit which is thefundamental means of this invention is first described in detail, andthen an industrial scale isotope separation apparatus comprising anumber of such developing units and the operation procedure of theapparatus are explained.

It is known in the prior art that an adsorption zone of an isotopemixture is formed in a developing column packed with an adsorbent andthe isotope adsorption is developed with a suitable eluent, wherebyisotopes are separated while the adsorption zone migrates through thecolumn. For example, according to the processes described in JapanesePatent Application (OPI) Nos. 12,700/'72; 57,297/'74, etc., a developingcolumn packed with an ion exchange resin is regenerated beforehand withan appropriate oxidizing agent or a reducing agent, a uranium adsorptionzone is formed in the column, the uranium zone is developed by an eluentsuch as an aqueous solution of an oxidizing agent, a reducing agent,etc., to form a concentration gradient of the uranium isotopes in theuranium adsorption zone, and the portion of the adsorbed uranium havingthe desired composition is collected from the column. Also, F. H.Spedding, "Laboratory Method of Nitrogen Ion Separation of Ion ExchangeResin", J. Amer. Chem. Soc., 77, 6125-6132 (1955) describes in detail aprocess in which an aqueous ammonium hydroxide solution containingnitrogen isotopes ¹⁴ N and .sup. 15 N is passed through a cationexchange resin-packed column which has been washed and regeneratedbeforehand with a dilute mineral acid to form an ammonium adsorptionzone and the adsorption zone is developed using an aqueous sodiumhydroxide solution as the eluent to form an isotope concentrationgradient in the adsorption zone.

Also, according to the investigations by the inventors of the presentinvention, boron isotopes can be separated in the same manner. That is,after a column packed with a strongly basic anion exchange resin hasbeen regenerated with an aqueous strong alkali solution such as anaqueous sodium hydroxide solution, an aqueous solution of boric acidcontaining boron isotopes ¹⁰ B and ¹¹ B is passed through the column toform a boric acid adsorption zone. Then, the boric acid adsorption zoneis developed using an aqueous strong acid solution as the eluent,whereby a concentration gradient of the boron isotopes is formed in theadsorption zone. In this method, the anion exchange resin-packed column,once used for the development and in equilibrium with the aqueous strongacid solution as the eluent solution, is regenerated with an aqueousstrong alkali solution as the regenerating agent solution, so that thecolumn can be used again for adsorption and development.

Exemplary strong alkalis which can be employed as the regenerating agentin this invention include sodium hydroxide, potassium hydroxide andammonia solution. Exemplary strong acids which can be employed as theeluent in this invention include inorganic acids such as hydrochloricacid, sulfuric acid, phosphoric acid and nitric acid, and organic acidssuch as acetic acid and formic acid.

As is clear from the above description, the general procedure ofseparating isotopes from a mixture thereof using a developing columnpacked with an adsorbent is:

(1) to regenerate the packed column to a suitable state for thedevelopment of an adsorption zone of the isotope mixture,

(2) to form an adsorption zone of the isotope mixture in one end of thepacked column,

(3) to develop the adsorption zone in the column with a suitable eluentto form a concentration gradient of the desired isotope in theadsorption zone, and then

(4) to collect the portion of the adsorbed isotope having a desiredconcentration from the adsorption zone.

When the separation of isotopes is carried out in such a manner asdescribed above, to concentrate the isotope to a desired concentrationthe adsorption zone must be developed along a distance of several metersto several hundreds of meters due to the very low separation factor ofisotopes and, further, the amount of the isotope obtained in oneoperation is usually very small.

As is clearly understandable, it is difficult to provide such a longdeveloping distance with a single adsorbent-packed column. Furthermore,when a large amount of isotopes are separated on an industrial scale,the amount of isotopes which can be collected in one development islimited, and accordingly it is necessary to repeatedly perform a largenumber of developments.

In order to avoid such difficulties, adsorbent-packed column unitshaving an appropriate length obtained by dividing a developing distanceof, generally several tens to several hundreds of meters are preparedand a developing apparatus can be set up by connecting theadsorbent-packed column units to one another in series through conduits.Such a developing apparatus of the in-series type is operated in thefollowing manner.

That is, after the entire developing apparatus has been regenerated witha regenerating agent solution, an isotope adsorption zone is formed inthe first adsorbent-packed column unit and developed by an eluentsolution. After the migration of the isotope adsorption zone to thesecond adsorbent-packed column unit has been completed, the firstadsorbent-packed column unit is regenerated with a regenerating agentsolution and again an isotope adsorption zone can be formed.

In the same manner, the isotope adsorption zone in the secondadsorbent-packed column unit is developed with an eluent solution andthe isotope adsorption zone successively migrates into the third, thefourth and the subsequent adsorbent-packed column units. At this time,the second, the third, and the subsequent adsorbent-packed column unitsthrough which the initial isotope adsorption zone has passed must beregenerated with a regenerating agent solution. In repeating theseprocedures it is possible to perform development within a necessary ordesired distance using adsorbent-packed units successively connecting alarge number of adsorption zones in series.

When the above described developing apparatus is set up, the developingdistance extends over several hundreds of meters and accordingly,several tens to several hundreds of adsorbent-packed column units areused. It is not easy to connect in series such a large number ofadsorbent-packed column units thorugh multi-way valves and toappropriately control the entire system. Since a large number ofadsorbent-packed column units are connected in series to one another, ashutdown even in one adsorbent-packed column unit affects the operationof the entire system and to prevent such an accident eachadsorbent-packed column unit must be provided with, for example, abypass line. Clearly, the developing apparatus needing suchconsideration becomes much more complicated and, as a result, itsoperation and control becomes more difficult.

According to this invention, the above-described single adsorbent-packedcolumn can be divided into a plurality of developing units having 2 toseveral tens of adsorbent-packed columns and, by independently operatingand controlling each developing unit, isotopes of a desiredconcentration can be separated and collected while developing an isotopeadsorption zone. An example of a developing unit performing such adeveloping operation is illustrated in FIG. 1 of the accompanyingdrawings shown as 13 or 13' wherein adsorbent-packed columns areconnected to multi-way valves, conduits, and liquid-supply andliquid-discharge pipes. In such a developing unit, a continuousdeveloping circuit is formed among the adsorbent-packed columns of thedeveloping unit, whereby regeneration takes place in one column whileadsorption or development is conducted in other columns. If theregeneration is completed, the column is further used for the subsequentadsorption and elution steps. That is, by performing the regeneration,adsorption and elution steps in three columns, an isotope-adsorptionzone can be developed for an infinite distance through the continuousdeveloping circuit in one developing unit. When the adsorption zone ofan isotope mixture is developed using such an operation, an isotopeconcentration gradient is formed in the zone due to the interactionbetween the isotopes and the adsorbent. The isotope concentrationgradient increases with increased developing distances. When the isotopeconcentration gradient of the adsorption zone reaches a desired valueafter the adsorption zone is developed to a sufficient distance, theisotope of a desired composition can be collected with an eluent fromthe system using an appropriate means such as by switching flowdirections by valve operation. The remaining adsorption zone having aninsufficient isotope concentration can be further concentrated to adesired extent by further developing the adsorption zone in thedeveloping unit. Moreover, by supplying an isotope mixture to theadsorption zone in the column in an amount corresponding to that of theisotopes removed from the column, the total amount of the isotopemixture in the adsorption zone can be always maintained at the samevalue. That is, the isotope adsorption zone formed in a part of aplurality of adsorbent-packed columns of the developing unit can bedeveloped along an infinite distance in the developing unit byalternately repeating the regeneration, adsorption and elutionoperations in the adsorbent-packed columns forming the developing unit,while collecting suitably the isotope enriched portion having thedesired concentration of the adsorption zone from the column andsupplying at the same time an isotope mixture in the same amount as thecollected amount t o the adsorption zone. Thus, the isotope can beseparated in a suitably concentrated state from the isotope mixture.

The superiority of the developing units according to this invention overthe above-described developing apparatus composed of adsorbent-packedcolumn units, each connected in series, is obvious. Using the developingunits of this invention, each of the developing units forms a closedcircuit by a continuous developing circuit whereby adsorbent-packedcolumns are connected to one another, and a predetermined amount ofisotopes can be separated and collected by infinitely circulating anisotope adsorption zone in the closed circuit. Therefore, each of thedeveloping units can be independently operated and controlled, and, as aresult, the procedures of operation are simple and an accident orshutdown in one developing unit does not affect the operation of otherdeveloping units. The developing units can be provided in paralleldepending upon the scale of the plant and the design and construction ofthe plant for the separation of isotopes become very easy. Theseadvantages cannot be expected of the above-described conventionaldeveloping apparatus of the in-series type.

The present invention provides an industrial scale isotope separationapparatus and isotope separation process, which can be controlled easilyin a simple manner by combining a plurality of such a developing unit asdescribed above in detail. That is, according to this invention, byconnecting the above-described developing unit to the liquid-supply mainpipes for a regenerating agent solution, an isotope mixture solution,and an eluent solution through flow rate regulators, the isotopeseparation can be performed independently in each developing unit whilesupplying thereto the solution from liquid-supply main pipes. In thiscase, pumps do not need to be provided for each developing unit forsupplying and circulating the solutions, since each solution to thedeveloping unit is supplied through liquid-supply main pipes. In anextreme case, the isotope separation apparatus comprising a plurality ofdeveloping units can be operated by equipping one liquid-supply pump toeach liquid-supply main pipe. This is one of the remarkable advantagesof this invention.

The advantage of this invention will be further clarified by comparing aconventional isotope separation apparatus and the isotope separationapparatus of this invention. In separating uranium-235 by theconventional gaseous diffusion method as described previously, about1400 separation units, each comprising one compressor and one diffuser,must be connected in series, and hence 1400 compressors are required inthe overall separation system. On the other hand, in this invention, oneliquid-supply pump for each liquid-supply main pipe is required for alarge number of developing units connected to the liquid-supply mainpipes. That is, only three pumps are required in this invention while1400 compressors are required in the conventional gaseous diffusionsystem. Generally, a large part of the maintenance work in a plantdepends upon the number of rotary machines utilized, so that there is noargument that this invention provides a superior isotope separationprocess to the conventional separation methods. This comparison is alsotrue for the gas centrifuge process. The superiority of this inventionwill be clearly understood by comparing the gas centrifuge process usingseveral hundred thousands of high-speed centrifuges with the isotopeseparation process of this invention using only a few liquid-supplypumps.

In the invention, the developing unit is usually connected to eachliquid-supply main pipe through a flow rate regulator. When anadsorption zone is being developed by the stream of an eluent solution,the developing rate of the adsorption zone is proportional to the flowrate of the eluent solution. Also, the isotope separation factordecreases as the developing rate increases. In order to attain the samedegree of separation in each developing unit, the developing rate of theadsorption zone is most easily controlled by the flow rate regulator.Each developing unit typically comprises 2 to 20 adsorbent-packedcolumns, conduits connecting them, and multi-way valves, and hence theflow resistance is not always uniform in each developing unit. Also, thenumber of adsorbent-packed columns through which an eluent passes at thedeveloping operation changes from time to time, resulting in afluctuation in the flow rate of the eluent solution even though theeluent is supplied to the developing unit from the liquid-supply mainpipe at a constant pressure. In order to avoid this fluctuation, it isdesirable to equip each developing unit with a flow rate regulator. Asis clear from the above explanation, the flow rate regulator preferablyfunctions to automatically maintain the flow rate of the supplied liquidconstant. To supply a solution at a constant flow rate from main pipesto each developing unit, equipping each developing unit with a meteringpump must be considered but it is desirable to equip each developingunit with a flow rate regulator rather than a metering pump.

The flow rate regulator which can be employed in this invention is alsouseful for other purposes. When two sets of developing units, A and B,are connected to the same liquid-supply main pipe and the same isotopemixture solution is supplied to both developing units while obtainingthe isotope at different concentrations as the products, it is mostdesirable to change the developing rate in each developing unit bycontrolling the flow rates of the eluent solution in each developingunit. In the system as described above, an isotope product with a highseparation degree is obtained from the developing unit operating at alow developing rate, while an isotope product with a low separationdegree is obtained from the developing unit operating at a highdeveloping rate. As a matter of course, when the developing rate ishigh, a larger amount of the product is obtained. The developing ratedirectly influences the concentration of the isotope in the product, andthus, it is desirable to employ a flow rate regulator which can befinely adjusted depending on the concentration of the product. As willbe explained hereinafter, the separation efficiency of the entireseparation apparatus is reduced by mixing if the isotope products ofeach unit collected through a common liquid-discharge main pipe havedifferent concentrations. Therefore, when the isotope products from eachdeveloping unit are collected in a common liquid-discharge main pipe,the concentrations of the isotope products produced by each developingare desirably maintained unit at the same value. For this purpose, it isparticularly preferred to connect a means capable of detecting at anytime the concentration of the isotope to each developing unit, and tocontrol precisely the flow rates according to the concentration thusdetected. In the case of a uranium isotope separation apparatus, thecomposition of ²³⁵ U and ²³⁸ U can be quickly determined by measuringthe gamma ray spectra, whereby the flow rate of an eluent solution canbe automatically controlled according to the concentration detected.

The developing rate of an adsorption zone is an important factor forcontrolling the operation of the entire separation apparatus. One of thepreferred embodiments of this invention is to equip the liquid-supplymain pipe with a pressure regulator for reducing the fluctuation of theflow rate during the operation to as small as is possible since thedeveloping rate of the adsorption zone is an important factor forcontrolling the operation of the entire apparatus. Various types ofpressure regulators can be employed for this purpose. The simplestpressure regulator is one in which the pressure in the main pipe ismaintained constant by overflowing a part of the liquid passing throughthe main pipe across a header provided at the upper portion thereof.However, the pressure in the liquid-supply main pipe should be usuallymaintained at 10 to 60 kg/cm², and thus this simple approach is notsuitable. One embodiment of the pressure controller which can be usedinvolves equipping the down stream of a liquid-supply pump with apressure control valve which is adjusted by detecting the pressure inthe liquid-supply main pipe. Another embodiment of the pressurecontroller is a system of supplying excessive liquid from theliquid-supply pipe through the pressure control valve placed in theby-pass line to a liquid-supply tank or the liquid-discharge main pipe.

Generally, three liquid-supply main pipes are employed for solutionssuch as regenerating agent solution, isotope mixture solution, andeluent solution. However, the solutions are not always supplied from thethree systems of the liquid-supply main pipes to the same developingunit. For example, frequently the mass flow of the eluent solution ismuch larger than that of the regenerating solution or the isotopemixture solution. In such a case, two or more liquid-supply systems forthe eluent solution may sometimes be employed per main pipe for each ofthe regenerating solution and the isotope mixture solution. Also, when alarge number of developing units are separated into two groups operatedwith different isotope compositions as feed materials, two liquid-supplymain pipes for an isotope mixture solution of different compositions areemployed per liquid-supply main pipe for each of the regenerating agentsolution and the eluent solution.

Furthermore, the number of liquid-supply main pipes connected to onedeveloping unit means is not necessarily three. When an adsorbent-packedcolumn in which development has been completed is regenerated by passinga regenerating agent solution through the column, two or more differentregenerating agents may be used to reduce the period of time requiredfor regeneration. For example, in a uranium isotope separation procedureusing an anion exchange resin as the adsorbent, the packed column inwhich development has been completed is regenerated using an aqueoussolution of an oxidizing agent. In this case, to reduce the regenerationperiod of time, a method is sometimes employed in which an oxidizingagent solution having a high concentration is first supplied to thecolumn for a short period of time to regenerate the greater part of theanion exchange resin and then an oxidizing agent solution of a suitableconcentration is supplied to complete the regeneration of the packedcolumn. In such a case, the liquid-supply main pipes connected to thedeveloping unit are two main pipes for the regenerating agent solutions,one main pipe for an isotope mixture solution and one main pipe for aneluent solution. It is clear that the individual operational controlscheme of each developing unit is not basically changed even if thenumber of liquid-supply main pipes is changed.

The features of this invention have been described above by referringmainly to the liquid-supply systems to each developing unit. Alsovarious techniques in handling the waste solutions discharged from eachdeveloping unit can be used. Usually, the waste solution containing theregenerating agent and the waste solution containing the eluent arecollected in a liquid-discharge main pipe and discarded therefrom orrecycled as it is or after appropriate treatment thereof. For example,in separating uranium isotopes using adsorbent-packed columns with ananion exchange resin, an oxidizing agent and a reducing agent used as aregenerating agent and an eluent, respectively, are deactivated afterdevelopment and discharged from the developing unit. They are collectedin a liquid-discharge pipe and are reused after being activated in anreactivation process. Furthermore, where two different regeneratingsolutions are used in the regeneration of an ion exchange resin columnas described above, at least five liquid discharge main pipes areemployed since two liquid-discharge main pipes for the first and thesecond regenerating agent solutions; one liquid-discharge main pipe forthe deactivated regenerating agent and eluent; and at least twoproducts-recovery main pipes are used. Reactivated regenerating agentand eluent are separated from each other and they can be used repeatedlyafter activating them separately. The operation of the developing unitsconnected in parallel to the liquid-discharge main pipes can beperformed without any particular restriction because of the number ofpipes used. These liquid-discharge main pipes can be open troughs butusually closed pipes are used for preventing the solution passingtherethrough from being contaminated or evaporated and applying anappropriate back pressure to the packed columns. In addition, tostabilize the flow rate in each developing unit to maintain the backpressure thereof can be maintained uniform and hence, if necessary, thepressure in the pipes is maintained by equipping the liquid-dischargepipe with a pressure regulator.

Two liquid-discharge main pipes are usually employed for collecting theisotope-enriched product from the developing unit. An isotope mixture ofnitrogen, boron, or uranium, i.e., containing ¹⁴ N and ¹⁵ N, ¹⁰ B and ¹¹B, or ²³⁵ U and ²³⁸ U can be separated by the isotope separationapparatus of this invention, and two isotope products are dischargedfrom the apparatus. Further, two or more different products, eachcontaining the same isotope at a different concentration, can beobtained, if desired. One example of this is enriched uranium for alight water nuclear reactor from natural uranium containing about 0.7%²³⁵ U as the raw material can be obtained. The concentration of ²³⁵ U inthe product is selected in the range of 2 to 4% in accordance with thispurpose. In such a case, a common liquid-discharge main pipe isconnected to each developing unit discharging the same product assay.Isotope products of different assay are recovered separately by eachliquid-discharge pipe. Even in this case, the liquid-supply pipes andliquid-discharge pipes for the regenerating agent or the eluent may beconnected to the entire developing unit.

The isotope mixtures which can be separated according to this inventionare not limited to nitrogen, boron, or uranium isotopes. This inventionis also applicable to any isotope mixtures capable of forming anadsorption zone on a pre-regenerated adsorption and wherein an isotopeconcentration gradient can be developed in the adsorption zone by usinga suitable eluent. Examples of such isotopes are isotope mixtures of ⁴⁶Ti and ⁴⁸ Ti; ⁵⁴ Fe and ⁵⁶ Fe; and ²⁰⁶ Pb and ²⁰⁸ Pb in addition to theabove-illustrated isotope mixtures.

Any adsorbents which can apparently selectively adsorb thereon part ofan isotope mixture in the isotope adsorption zone can be used as theadsorbent in this invention. Examples of such adsorbents are cationexchange resins, anion exchange resins and adsorbents obtained bysupporting a substance having selective adsorbability such as crowncompounds, liquid ion exchangers, etc. on a porous carrier such assilica, alumina, zeolite, etc. Cation exchange resins used in thisinvention are not limited, and include, for example, strongly acidiccation exchange resins prepared by introducing sulfo groups intostyrene-divinylbenzene copolymers and weakly acidic cation exchangeresins prepared by introducing carboxylic groups intostyrene-divinylbenzene copolymers, which preferably have a degree ofcrosslinking of more than about 4%. Anion exchange resins used in thisinvention include, for example, strongly basic anion exchange resinshaving quaternary ammonium groups therein prepared by chloromethylatingstyrene-divinylbenzene copolymers, followed by amination; weakly basicanion exchange resins having primary, secondary or tertiary amine groupstherein; and nitrogen-containing heterocyclic compounds, whichpreferably have a degree of crosslinking of more than about 4%.

An example of this invention will be explained in greater detail byreference to the accompanying drawings.

FIG. 1 shows a typical embodiment of the isotope separation apparatus ofthis invention wherein a developing unit composed of threeadsorbent-packed columns are connected to three liquid-supply main pipesand foud liquid-discharge main pipes.

In FIG. 1, numerals 1 to 3 represent storage tanks; numerals 4 to 6liquid-supply pumps; numerals 7 to 9 pressure regulators, and numerals10 to 12 liquid-supply main pipes for a regenerating agent solution, anisotope mixture solution, and an eluent solution, respectively. Numerals13 and 13', each represents a set of developing units and numerals 14,15 and 16 represent flow rate regulators equipped to the liquid-supplybranch pipes 17, 18 and 19, respectively.

The separation of isotopes is explained by referring to FIG. 1. It willbe assumed that in the three adsorbent-packed columns 23, 24 and 25 ofthe developing unit 13, a developing operation is being conducted inpacked column 24, an adsorption operation is being conducted in packedcolumn 25, and the developing operation has just been finished in packedcolumn 23. Since the subsequent operation of column 23 is theregeneration of the adsorbent, a regenerating agent solution is suppliedto column 23 through branch pipe 17 and a multi-way valve 200 toregenerate the adsorbent in column 23. The eluent solution remaining incolumn 23 is collected in a waste eluent tank 40 through a multi-wayvalve 260, a liquid-discharge branch pipe 30, and a liquid-dischargemain pipe 35. When the eluent solution in packed column 23 is entirelyreplaced with the regenerating agent solution from the column, themulti-way valve 260 is operated to collect the regenerating agentsolution from the column in waste regenerating agent tank 39 through abranch pipe 29 and a main pipe 34.

Packed column 23 whose regeneration has been completed is used in thesubsequent adsorption operation. That is, after collecting two differentisotope products from the isotope adsorption zone formed in packedcolumn 25 in product tanks 41 and 42, respectively, through a multi-wayvalve 280, the remaining isotopes in the adsorption zone are sent tocolumn 23 through a continuous developing circuit composed of a valve280, a continuous pipe 33, and a valve 200. An isotope mixture solutionof the same amount removed from column 25 is supplied to column 25through a liquid-supply branch pipe 18 and a valve 200. The solutionthus supplied forms an adsorption zone in column 23 together with theisotopes supplied from column 25. The feeding time of the isotopemixture through the liquid-supply branch pipe 18 as a raw material is soadjusted that is does not disturb the concentration gradient of isotopescirculated from the column 25. To achieve this condition where no mixingoccurs a method is employed in which the feeding moment where theisotope concentration of the solution passing through the valve 200 isthe same as that of the feed material is selected, while isotopeconcentration varies from time to time. One method to accomplish thiscomprises temporarily stopping the flow of isotope solution circulatingfrom column 25 at the feeding moment, and then to supply fresh feed of asuitable amount through the valve 200. The flow of isotope solution fromcolumn 25 is then resumed after adding fresh feed. Thus, theregenerating agent solution filled in column 23 by such an adsorptionprocedure is collected in a waste regenerating agent tank 39 through avalve 260, a liquid-discharge pipes 29 and 34. The adsorption zone ofthe isotope mixture thus formed in column 23 is developed by the eluentsolution to perform a separation of the isotopes. That is, theadsorption zone formed in column 23 flows down slowly through column 23by the effect of the eluent solution supplied into column 23 throughliquid-supply main pipe 12, branch pipe 19, and multi-way valve 200. Aslight difference between the apparent migration rate of the isotopesincreases the concentration gradient in the adsorption zone. Through thedeveloping operation, the regenerating agent solution or a mixture ofthe regenerating agent solution and the eluent solution emerging frompacked column 23 is collected in a waste regenerating agent tank 39 or awaste eluent tank 40, respectively. When the adsorption zone flowingdown through column 23 reaches the bottom thereof, the isotope mixtureis sent to column 24 where the regneration has completed, by operatingmulti-way valves 260 and 210. Thus the operations for adsorption anddevelopment are continued.

In developing unit 13' in FIG. 1, each numeral having a prime "'"designation has the same meaning as numeral without a prime designationin developing unit 13. For example, numeral 23' denotes anadsorbent-packed column which is the counterpart of numeral 23 in thedeveloping unit 13.

The function of each developing unit is clear from the aboveexplanation. In this invention, a number of such developing units areconnected in parallel to the liquid-supply main pipes through flow rateregulators 14, 15 and 16; 14', 15' and 16'; etc. The flow rateregulators control the flow rates of the regenerating agent solution,the isotope mixture solution, and the eluent solution to predeterminedvalues and are particularly important for securing a stable operation ofeach developing unit. In particular, when the multi-way valve of eachcolumn is operated using a timer, an appropriate switch-over time mustbe maintained to keep the flow rate stable. Also, pressure regulators 7,8 and 9 equipped in the liquid-supply main pipes are important andeffective for this purpose.

The number of the adsorbent packed columns in each developing unit maybe suitably selected in the range of 2 to 20. In order to maintain acontinuous developing operation, one of the adsorbent packed columnsmust be in a regeneration operation and one of them must be in a waitingstate after finishing the regeneration, and even if the two operationsare performed in one column, at least two packed columns are necessaryin the same developing unit. If the number of adsorbent-packed columnsis larger, the developing operation, that is, the ratio ofadsorbent-packed columns used, for isotope separation becomes higher.However, on the other hand, if the number of adsorbent-packed columnsincreases, multi-way valves, piping, etc., become more complicatedincreasing the construction cost. Due to such reasons, the number ofadsorbent-packed columns used in each developing unit is typically 2 to20, and preferably 3 to 8.

These adsorbent-packed columns may be disposed on the same level or theymay be disposed in the form of a single column. Briefly, theconfiguration of the adsorbent-packed columns may be designed from thestandpoints of reduction in construction cost, and efficiency ofworking. However, the configuration of the adsorbent-packed columns isconsidered particularly so that the continuous piping between the firstcolumn to the next column is kept as short as possible and at a constantlength. When an adsorption zone of isotopes migrates from oneadsorbent-packed column to the subsequent adsorbent-packed column due tothe development operation, the isotope concentration gradient in theadsorption zone is unavoidably reduced to some extent by the disturbanceof the liquid stream but the reduction can be kept at a minimum bydesigning the structure of the adsorbent-packed columns and the pipingfor connecting the both columns. In order to keep the reduction of theisotope concentration gradient at a minimum, the adsorbent-packedcolumns are desirably disposed at the same distance and as close aspossible. As a practical configuration, the packed columns belonging toeach unit developing means are disposed circularly at the same intervalor the packed columns are disposed in two or more rows.

FIG. 2 shows an example of the application of this invention, in whichactivating means 43 and 44 for a regenerating agent and an eluent areemployed in addition to the apparatus in FIG. 1. A used regeneratingsolution collected in a waste regenerating agent tank 39 from thedeveloping unit described above is treated in the activating means 43where impurities in the solution and water therein are removed to adjustthe concentration of the solution and then the regenerating agentsolution is supplied to a regenerating agent tank 1 through acirculation conduit 45. Also, the eluent collected in waste eluent tank40 is supplied to eluent tank 3 through activating means 44 and acirculation conduit 47. Frequently, the waste eluent solution gets mixedin a waste regenerating agent solution during regeneration ordevelopment but in such a case, both components are separated, purified,and activated in activating means 44 and then are circulated intoregenerating agent tank 1 and eluent tank 3, respectively. Also, theactivating means may be further connected in various other manners thanthe one described above depending on the manner of operation of thedeveloping unit.

FIG. 3 shows examples of pressure regulators in liquid-supply main pipesused in this invention. In FIG. 3, A is a system where the flow rate tothe main pipe is regulated using a pressure regulating valve and B is asystem where an excessive amount of liquid is flowed back to aliquid-supply tank using a pressure regulating valve. In FIG. 3, numeral1 denotes a liquid-supply tank; numeral 132 a liquid-supply pump;numeral 133 an automatic regulation valve; numeral 134 a pressuredetector in main pipe; numeral 135 an automatic valve regulator; numeral136 a liquid-supply main pipe; and numeral 137 a back flow conduit.

FIG. 4 shows an example of a system of connecting liquid-discharge mainpipes and the developing unit in this invention. In FIG. 4, varioussolutions are supplied to a developing unit 13 through liquid-supplymain pipes 10, 11, and 12, branch pipes 40, 50 and 60, cut-off valves70, 80, and 90, and automatic flow rate regulators 100, 110, and 120. Inaddition, numerals 130, 140 and 150 denote flow rate detectors andnumerals 160, 170 and 180 denote automatic valve regulators. Wastesolutions from the developing units are discharged in liquid-dischargemain pipes 34, 35, 36 and 37 through liquid-discharge branch pipes 201,211, 221 and 231 and cut-off valves 241, 251, 261 and 271.

The cut-off valves provided to the liquid-discharge branch pipes are forcutting off the developing unit from the liquid-discharge main pipes forinspection or repairing any accident which might occur in the developingunit, and can be operated by hand or by remote control. One remarkablefeature of this invention is that each developing unit ca be cut offwithout any influence on the operation of other developing units.

In separating and concentrating an isotope on a large industrial scaleusing the isotope separating apparatus of this invention, control of theoperation is easy and sure. For example, in concentrating uraniumisotope on an industrial scale, several to several thousands ofdeveloping units must be used and in such case the separation andconcentration of the uranium isotope can be carried out in a stablemanner by separately controlling the pressure in the liquid-supply mainpipes and the flow rate to each developing unit. The operation of themulti-way valves of each developing unit can be easily performed byemploying a simple automatic regulator connected to an automaticanalyzer, an integrating indicator for solution flow rate, a timer, etc.For this purpose, various operational control methods of each developingunit can be employed in this invention. Most practically, aconcentration detector is provided between one adsorbent-packed columnand the subsequent adsorbent-packed column with the continuousdeveloping circuit. The detector detects the front end and the rear endof an isotope solution and the multi-way valve positioning in front ofthe detector can be appropriately operated by the signals of thedetector. At this time, a timer is operated by the signals of thedetector, and then the multi-way valve can also be operated after apredetermined period of time upon detection of the front end and therear end of an isotope solution. Since the flow amount of an eluentsolution is precisely proportional to the migration distance of anisotope adsorption zone in an adsorbent-packed column, the multi-wayvalve can also be operated by the concentration detector in combinationwith an integrating flow amount of the eluent solution. The controlmethod of using the integrating flow amount of the eluent solution ismore precise than that of using a timer, especially when there is afluctuation in the flow rate of the eluent solution.

Any type of concentration detectors capable of detecting the boundarybetween a regenerating agent solution and an isotope mixture solution orthe boundary between an isotope mixture solution and an eluent solutioncan be employed in this invention. The concentration detectors whichadapt any principle such as electric conductivity, adsorbance,refractive index and oxidation-reduction potential can be employed. Ofthese detectors, a detector adapting the principle of adsorbance ispreferred due to its precision, its shortness in response and its lowcost. Since an individual automatic regulating device is employed ineach developing unit, a central automatic controlling means for watchingor controlling the entire plant is substantially unnecessary in thisinvention, which is also one of the remarkable features of thisinvention.

The following examples are given to illustrate the present invention ingreater detail.

EXAMPLE 1

Two sets of developing units, each comprising four adsorbent-packedcolumns as shown in FIG. 5, were prepared. In FIG. 5, numerals 1, 2 and3 denote storage tanks for an isotope mixture solution, a regeneratingagent solution, and an eluent solution, respectively; numerals 4, 5 and6 liquid-supply pumps; numerals 70 and 80 back pressure valves; andnumerals 10, 11 and 12 liquid-supply main pipes. To these liquid-supplysystems were connected two sets of developing units comprising fouradsorbent-packed columns 23, 24, 25 and 26 and four adsorbent-packedcolumns 23', 24', 25' and 26', respectively, through flow rate controlneedle valves 120, 130 and 140 and 120', 130' and 140', and also flowrate meters 15 and 16 and 15' and 16', respectively. In FIG. 5, numerals200, 210, 220, 280, 290, 300 and 310 and 200', 210', 220', 230', 280',290', 300' and 310' denote multi-way valves; numerals 17, 18 and 19 and17', 18' and 19' denote liquid-supply branch pipes; numerals 31, 32 and33 and 31', 32' and 33' denote liquid-discharge branch pipes; andnumerals 320, 330, 340 and 350 and 320', 330', 340' and 350' denoteconnecting pipes. Also, numerals 34, 35 and 36 denote liquid-dischargemain pipes common to both developing units and the main pipes wereconnected to a sampling fraction collector 42, a waste regeneratingagent storage tank 143, and a waste eluent solution storage tank 144,respectively.

Each adsorbent-packed column was composed of a Pyrex glass-jacketedchromato-tube of an inside diameter of 30 mm and a height of 1200 mmwith distributors at both ends, the tube being densely packed with aporous, tertiary amine-type, strongly basic anion exchange resin havingan exchange capacity of 0.7 milliequivalent/ml. wet resin and a particlesize of 100 to 200 mesh (Tyler standard sieve) upto a packed height of1000 mm.

Then, the isotope mixture solution, the regenerating agent solution andthe eluent solution having the compositions shown below were heated to80° C. in storage tanks 1, 2 and 3, respectively, and supplied toliquid-supply main pipes by means of liquid-supply pumps, 4, 5 and 6,respectively. The excessive solutions thus supplied flowed back to eachstorage tank through the back pressure valves 70 and 80 and thepressures in the liquid-supply main pipes were always maintained atabout 15 kg/cm². In this case, however, only the liquid-supply pump 4for the isotope mixture solution was driven only when the solution wassupplied to the packed columns.

Isotope Mixture Solution: An aqueous solution of natural uraniumcontaining 0.025 M of uranous chloride and 4.0 M of hydrobromic acid.

Regenerating Agent Solution: An aqueous solution containing 0.05 M offerric chloride and 4.0 M of hydrobromic acid.

Eluent Solution: An aqueous solution containing 0.05 M of titaniumtrichloride and 4.0 M of hydrobromic acid.

By using the above described apparatus, the following developingoperation was performed. More specifically, the regenerating agentsolution was supplied to the resin-packed columns, previously washedsufficiently with an aqueous solution containing 4 M of hydrobromicacid, through valve 130, flow rate meter 15, liquid-supply branch pipe18, and multi-way valves 200, 210, 220 and 230 to saturate the resin inthe columns with ferric chloride. The waste regenerating agent solutionfrom the columns was collected in storage tank 143 through multi-wayvalves 280, 290, 300 and 310, liquid-discharge branch pipe 32, andliquid-discharge main pipe 35. Then, the isotope mixture solution wasintroduced into the top of packed column 23 through valves 120 and 200,whereby uranium isotopes were adsorbed on the resin in the column whilereplacing ferric ions to form an adsorption zone. The flow rate of theuranium-containing solution was controlled in such a manner that thefront end of the uranium adsorption zone flowed down through theresin-packed column at a rate of 30 cm/hr. When the front portion of theuranium adsorption zone reached the bottom of column 23, the uraniumsolution was introduced into column 24 by operating multi-way valves 280and 210 through connecting pipe 320 to form a uranium adsorption zone incolumn 24 while replacing with ferric chloride. Then, when the front endof the uranium adsorption zone had reached the lower end of column 24,the supply of the uranium isotope mixture solution was stopped. Duringthe operation, the waste regenerating agent solution from columns 23 and24 was collected in storage tank 143 through the liquid-discharge mainpipe.

Then, the eluent solution was introduced into the packed column throughneedle valve 140, flow rate meter 16, and multi-way valve 200 and thusthe uranium-adsorption zone formed in the previous step was developed incolumns 25 and 26. Thus, the uranium-adsorption zone successivelymigrated to the subsequent column through connecting pipes 330 and 340and when the front end of the uranium-adsorption zone had reached thebottom of column 26, the zone was flowed back to column 23 throughconnecting pipe 350. During this step, the regenerating agent solutionwas introduced into columns 23 and 24, in which development had beencompleted, through liquid-supply branch pipe 18 by operatingsuccessively multi-way valves 23 and 24, whereby the eluent solutionremaining in the columns was replaced with the regenerating agentsolution for the subsequent development. At this time the used eluentsolution was led to waste eluent solution storage tank 144 throughmulti-way valve 290, liquid-discharge branch pipe 33 and thenliquid-discharge main pipe 36.

Thus, after developing the uranium-adsorption zone formed in columns 23and 24 twice per column or for a total of eight columns, theuranium-adsorption zone was withdrawn from the bottom of column 26 bythe operation of multi-way valve 310. The uranium solution thuswithdrawn was successively partitioned into 200 ml fractions andcollected through liquid-discharge branch pipe 31 and thenliquid-discharge main pipe 34 in fraction collector 42, a part of whichwas subjected to a quantitative analysis of uranium and massspectrometry of the isotopic analysis of 235_(U).

In the fractions thus sampled, the uranium amount and the abundanceratio of ²³⁵ U/²³⁸ U in the first fraction and the final fraction of theparts containing uranium were as follows.

                  TABLE 1                                                         ______________________________________                                        Results of Operation of First Developing Unit                                             Uranium  Abundance Ratio                                                      Amount   of                                                                   (mg)     .sup.235 U/.sup.238 U                                    ______________________________________                                        First Fraction                                                                              673        0.006829                                             Final Fraction                                                                              565        0.007815                                             ______________________________________                                         The abundance ratio of .sup.235 U/.sup.238 U in the natural uranium was       0.007252.                                                                

Also, while performing the above described isotope separation operationin the first developing unit, the developing operation of anotheruranium adsorption zone was performed at the same time in the seconddeveloping unit described in FIG. 5. In the second developing unit, eachnumeral with a prime "'" designation in FIG. 5 denotes the same meaningas the numeral without a prime "'" designation in the first developingunit. For example, numeral 23' denotes an adsorbent-packed column in thesecond developing unit which is the counterpart of numeral 23 in thefirst developing unit. In this case, the operation conditions were thesame as those in the first developing unit except that the flow rates ofthe uranium isotope mixture solution and the eluent solution wereincreased to adjust the migration ratio of the uranium adsorption zoneto 20 cm/hr. After developing the uranium adsorption zone to a totaldistance of 8 meters, the uranium adsorption zone was withdrawn frompacked column 26' through the multi-way valve 310' and the uraniumsolution thus withdrawn was partitioned into 200 ml fractions andcollected in fraction collector 42. A part of the fractions wassubjected to a quantitative analysis of uranium and mass spectrometry ofthe isotopic analysis of ²³⁵ U. The uranium amount and the abundanceratio of ²³⁵ U/²³⁸ U in the first fraction and the final fraction ofparts containing uranium in the sampled fractions are set forth in Table2 below.

                  TABLE 2                                                         ______________________________________                                        Results of Operation of Second Developing Unit                                            Uranium  Abundance Ratio                                                      Amount   of                                                                   (mg)     .sup.235 U/.sup.238 U                                    ______________________________________                                        First Fraction                                                                              741        0.006632                                             Final Fraction                                                                              690        0.007981                                             ______________________________________                                    

EXAMPLE 2

In each of packed columns 23, 24, 25 and 26 and 23', 24', 25' and 26' ofthe same isotope separation apparatus as described in Example 1 wasdensely packed a strongly acid cation exchange resin ("Amberlite 200",manufactured by Rohm & Haas Co.) of 100 to 200 mesh (Tyler standardsieve) at a height of 1000 mm. Then, the isotope mixture solution, theregenerating agent solution and the eluent solution having thecomposition shown below were stored in storage tanks 1, 2 and 3,respectively, and supplied to liquid-supply main pipes by means ofliquid-supply pumps 4, 5 and 6.

Isotope Mixture Solution: An aqueous solution containing 0.6 M ofammonium hydroxide.

Regenerating Agent Solution: An aqueous solution containing 2 M ofhydrochloric acid.

Eluent Solution: An aqueous solution containing 0.6 M of sodiumhydroxide.

Excessive portions of the solutions thus supplied flowed back to eachstorage tank through back pressure valves 70 and 80 and the pressure inthe liquid-supply main pipes was always controlled at about 15 kg/cm².In this case, however, liquid-supply pump 4 only for the isotope mixturesolution was driven only when the solution was supplied to the packedcolumns but was stopped in other cases.

The separation of nitrogen isotopes ¹⁴ N and ¹⁵ N was performed usingthe above-described apparatus employing the following operations. Thatis, the ion exchange resin-packed columns were sufficiently washed withthe regenerating agent solution. Then, the nitrogen isotope mixturesolution, i.e., an aqueous solution containing of 0.6 M of ammoniumhydroxide, was introduced into packed column 23 through valves 120 and200 to form a nitrogen adsorption zone. When the front end of theadsorption zone had reached the bottom of the column, the isotopemixture solution was introduced to packed column 24 through connectingpipe 320 to form also a nitrogen adsorption zone in column 25. Throughthe adsorption procedure, the flow rate of the isotope mixture solutionwas controlled by valve 120 in such a manner that the front end of theadsorption zone flowed down through the column at a rate of about 40cm/hr.

Thereafter, the eluent solution was introduced into packed column 23through needle valve 140, flow rate meter 16, and multi-way valve 200 todevelop the nitrogen adsorption zone formed in the previous step tocolumns 25 and 26. In this case, the nitrogen adsorption zonesuccessively migrated to the subsequent columns through connecting pipes330 and 340, and when the front end of the adsorption zone had reachedthe bottom of column 26, the adsorption zone flowed back to column 23through connecting pipe 350. The column, in which the developingoperation had been completed, was subjected to the regenerationoperation as described in Example 1 for the subsequent development.

After developing the nitrogen adsorption zone twice per column or for atotal of eight columns as described above, the nitrogen adsorption zonewas withdrawn from the bottom of packed column 26 and successivelypartitioned into 200 ml fractions and collected in fraction collector42. These solutions thus collected were used as samples for aquantitative analysis of ammonium hydroxide and a mass spectrometry ofthe isotopic analysis of ¹⁵ N.

The ammonium concentration and the abundance ratio of ¹⁵ N/¹⁴ N in thefirst fraction and the final fraction of portions containing ammoniumhydroxide in the sampled fractions were as follows.

                  TABLE 3                                                         ______________________________________                                        Results of Operation of First Developing Unit                                                       Abundance Ratio                                                    Ammonium   of                                                                 Concentration                                                                            .sup.15 N/.sup.14 N                                     ______________________________________                                        First Fraction                                                                             0.53 N       0.00043                                             Final Fraction                                                                             0.48 N       0.0298                                              ______________________________________                                         The abundance ratio of .sup.15 N/.sup.14 N in the natural ammonium            hydroxide used was 0.00365.                                              

Also, while performing the isotope separation described above in thefirst developing unit, the development of another nitrogen adsorptionzone was simultaneously performed in the second developing unitdescribed in FIG. 5. In this case, the operation conditions were thesame as those in the first developing unit except that the flow rates ofthe aqueous ammonium hydroxide solution and the eluent solution wereincreased to control the migration ratio of the nitrogen adsorption zoneto 75 cm/hr. After developing the nitrogen adsorption zone to a totaldistance of 8 meters, the nitrogen adsorption zone was withdrawn fromthe system through column 26' and the solution was partitioned into 200ml fractions and collected in the fraction collector 42. The ammoniumconcentration and the abundance ratio of ¹⁵ N/¹⁴ N in the first fractionand the final fraction of portions containing ammonium hydroxide in thesampled fractions were as follows.

                  TABLE 4                                                         ______________________________________                                        Results of Operation of Second Developing Unit                                                      Abundance Ratio                                                    Ammonium   of                                                                 Concentration                                                                            .sup.15 N/.sup.14 N                                     ______________________________________                                        First Fraction                                                                             0.49 N       0.00067                                             Final Fraction                                                                             0.45 N       0.0195                                              ______________________________________                                    

EXAMPLE 3

In each of packed columns 23, 24, 25 and 26 and 23', 24', 25' and 26' ofthe same isotope separation apparatus as described in Example 1 wasdensely packed a strongly basic anion exchange resin ("AmberliteIRA-40", manufactured by Rohm & Haas Co.) of 100 to 200 mesh (Tylerstandard sieve) to a height of 1000 mm. Then, the isotope mixturesolution, the regenerating agent solution and the eluent solution havingthe composition shown below were stored in storage tank 1, 2 and 3,respectively, and supplied to liquid-supply main pipes by means ofliquid-supply pumps 4, 5 and 6.

Isotope Mixture Solution: An aqueous solution containing 0.5 M of boricacid and an aqueous solution containing 8 percent by weight of glycerol.

Regenerating Agent Solution: An aqueous solution containing 1.0 M ofsodium hydroxide.

Eluent Solution: An aqueous solution containing 0.5 M of acetic acid andan aqueous solution containing 8 percent by weight of glycerol.

The supply and the pressure control of the solutions in theliquid-supply main pipes were carried out in the same manner as inExample 1.

The separation of boron isotopes ¹⁰ B and ¹¹ B was performed using theabove-described apparatus employing the same operations as described inExample 2. In this separation all the solutions were maintained at 40°C. That is, in the same manner as in Example 2, a boric acid adsorptionzone was formed in ion exchange resin-packed columns 24 and 25 which hadbeen sufficiently regenerated with the regenerating agent solution andsubsequently developed with the eluent solution in packed columns 25 and26. The packed-columns, in which development had been completed, weresuccessively regenerated with the regenerating agent solution forfurther forming a boric acid adsorption zone therein.

Thus, after developing the boric acid adsorption zone three times percolumn to a total distance of 12 meters in a migration ratio of about 40cm/hr as described above, the boric acid adsorption zone was withdrawnfrom the bottom of packed column 26 and successively partitioned into100 ml and collected in fraction collector 42. These solutions thuscollected were used as samples for a quantitative analysis of boric acidand mass spectrometry of the isotopic analysis of ¹⁰ B.

The boric acid concentration and the abundance ratio of ¹⁰ B/¹¹ B in thefirst fraction and the final fraction of portions containing boric acidin the sampled fractions were as follows.

                  TABLE 5                                                         ______________________________________                                        Results of Operation of First Developing Unit                                                       Abundance Ratio                                                    Boric Acid of                                                                 Concentration                                                                            .sup.10 B/.sup.11 B                                     ______________________________________                                        First Fraction                                                                             0.34 M       0.1229                                              Final Fraction                                                                             0.36 M       0.4837                                              ______________________________________                                         The abundance ratio of .sup.10 B/.sup.11 B in the natural boric acid used     was 0.2348.                                                              

The abundance ratio of ¹⁰ B/¹¹ B in the natural boric acid used was0.2438.

Also, while performing the isotope separation described above in thefirst developing unit, the development of another boric acid adsorptionzone was simultaneously performed in the second developing unitdescribed in FIG. 5. In this case, the operation conditions were thesame as those in the first developing unit except that the flow rate ofthe eluent solution was increased to control the migration ratio of theboric acid adsorption zone to 75 cm/hr. After developing the boric acidadsorption zone to a total distance of 12 meters, the boric acidadsorption zone was withdrawn from the system through column 26' and thesolution was partitioned into 100 ml fractions and collected in fractioncollector 42. The boric acid concentrations and the abundance ratio of¹⁰ B/¹¹ B in the first fraction and the final fraction of portionscontaining boric acid in the sampled fractions were as follows.

                  TABLE 6                                                         ______________________________________                                        Results of Operation of Second Developing Unit                                                      Abundance Ratio                                                    Boric Acid of                                                                 Concentration                                                                            .sup.10 B/.sup.11 B                                     ______________________________________                                        First Fraction                                                                             0.29 M       0.1476                                              Final Fraction                                                                             0.33 M       0.4026                                              ______________________________________                                    

While the invention is described in detail and with reference tospecific embodiments thereof, various changes and modifications can bemade therein by one skilled in the art without departing from the spiritand scope thereof.

What is claimed is:
 1. A process for separating isotopes employing anapparatus comprising a plurality of separation units assembled inparallel, each separation unit comprising at least two adsorbent-packedcolumns in series and forming a continuous developing loop, and at leastone common liquid-supply pipe connected to each separation unit througha liquid flow rate regulator, the process comprising supplying anisotope mixture solution to each separation unit through one of thecommon liquid-supply pipes, and continuously developing the isotopemixture serially and repeatedly through all the columns making up eachunit thereby to separate the isotopes.
 2. The process as claimed inclaim 1, wherein each separation unit is connected to threeliquid-supply main pipes, one for a regenerating agent solution, one foran isotope mixture solution, and one for an eluent solution.
 3. Theprocess as claimed in claim 2, wherein the process includes changing theflow rate of the eluent solution in each separation unit wherebyproducts having different isotope compositions are obtained.
 4. Theprocess as claimed in claim 2, wherein the adsorbent is an ion exchangeresin, the regenerating agent solution and the eluent solution each isan oxidizing agent solution or a reducing agent solution, and theisotope mixture solution is a uranium isotope solution.
 5. The processas claimed in claim 4, wherein the adsorbent is an anion exchange resin,the regenerating agent solution is an oxidizing agent solution, theeluent solution is a reducing agent solution, and the isotope mixturesolution is a uranium isotope solution.
 6. The process as claimed inclaim 2, wherein the adsorbent is a cation exchange resin, the isotopemixture solution is a nitrogen isotope mixture solution, theregenerating agent solution is an aqueous acid solution, and the eluentsolution is an aqueous alkali solution.
 7. The process as claimed inclaim 2, wherein the adsorbent is a strongly basic anion exchange resin,the isotope mixture solution is a boron isotope mixture solution, theregenerating agent is an aqueous strong alkali solution and the eluentsolution is an aqueous strong acid solution.